1. Field of the Invention
The present invention relates to a method of manufacturing an electronic component using a ceramic laminate. The present invention also relates to the structure of a variable capacitor.
2. Description of the Background Art
For example, a variable capacitor which is applied to a trimmer capacitor typically comprises a stator electrode, a rotor electrode which is rotated with respect to the same, and a dielectric which is arranged between the stator electrode and the rotor electrode. The dielectric is provided by a ceramic dielectric, for example.
In order to widen the range of capacitance adjustment in such a variable capacitor, it is necessary to increase the maximum acquirable capacitance. To this end, the dielectric which is arranged between the stator electrode and the rotor electrode is reduced in thickness. When the dielectric is formed of a ceramic dielectric, however, its thickness cannot be much reduced since the same has relatively low mechanical strength.
In order to solve this problem, either the stator electrode or the rotor electrode is formed in the interior of the ceramic dielectric. Thus, the ceramic dielectric is increased in thickness to be improved in mechanical strength, while the stator electrode and the rotor electrode are opposed to each other through a part of the ceramic dielectric so that the distance therebetween is reduced, thereby attaining a high maximum capacitance.
In relation to a variable capacitor of the aforementioned type comprising a stator electrode or a rotor electrode which is formed in the interior of a ceramic dielectric, Japanese Utility Model Publication No. 63-5223 (1988), for example, describes a variable capacitor having a stator electrode which is formed in the interior of a ceramic dielectric, in particular. In this variable capacitor, the ceramic dielectric having the stator electrode provided therein forms a stator, which is one of the basic elements of the variable capacitor, while a terminal is formed on the surface of this stator by a conductor film to be electrically connected to the stator electrode.
Further, a concave portion is formed in the lower surface of the stator which is formed by the ceramic dielectric, so that an engaging member provided on a cover for rotatably storing a rotor forming the rotor electrode engages on this concave portion. Therefore, the engaging member will not project beyond the lower surface of the stator, whereby the variable capacitor can be surface-mounted on a printed circuit board with no problem.
It is basically possible to manufacture the aforementioned stator, which is formed by a ceramic dielectric having a stator electrode provided therein, by a technique of manufacturing a multilayer ceramic capacitor. However, the technique of manufacturing a multilayer ceramic capacitor cannot be simply employed due to the presence of the concave portion, which is not necessary for a multilayer ceramic capacitor. While the aforementioned literature describes no method for obtaining such a stator, a ceramic dielectric for forming a stator may be provided with a shape for defining a concave portion in a stage before firing, to be then fired. In this method, however, it is anticipated that a specific step is required for forming the concave portion with requirement for a specific die or equipment, leading to increase in cost for the stator.
While a problem of the conventional manufacturing method has been described with reference to a variable capacitor, such a problem is not specific to the variable capacitor but may also arise in manufacturing of an electronic component using a ceramic laminate provided with a concave portion, such as a feed-through capacitor, a capacitor network, a high-voltage capacitor or a semiconductor package. This problem is particularly serious if the concave portion has a complicated shape.
Accordingly, an object of the present invention is to provide an improved method of manufacturing an electronic component using a ceramic laminate such as a variable capacitor, for example, which is adapted to enable manufacturing of a ceramic laminate, particularly that provided with a concave portion, by a method substantially similar to that for manufacturing a general multilayer ceramic capacitor.
In the variable capacitor described in the aforementioned literature, further, the stator electrode is formed by two semicircular split electrodes, while the rotor electrode is also formed by two semicircular split electrodes. The stator formed by the ceramic dielectric having the stator electrode therein is provided with two terminal electrodes, for serving as terminals, which are electrically connected to the two split electrodes forming the stator electrode respectively.
According to this variable capacitor, therefore, the two split electrodes forming the stator electrode and the those forming the rotor electrode form four electrostatic capacitances in total. Among these electrostatic capacitances, the first and second capacitances form a series circuit while the third and fourth capacitances form another series circuit, so that such two series circuits are connected in parallel with each other.
However, the variable capacitor of the aforementioned structure has the following problems to be solved:
First, the maximum capacitance cannot be appreciably increased. Since the stator electrode and the rotor electrode are formed by split electrodes respectively so that pairs of the as formed four capacitances are connected in series to each other respectively, the maximum capacitance is merely implemented by an electrostatic capacitance which is attained when quarter-circular electrodes are opposed to each other. Such a maximum capacitance is merely half that of a usual variable capacitor, which is implemented by an electrostatic capacitance attained when semicircular electrodes are opposed to each other.
Further, the capacitance is increased from the minimum to the maximum upon 90.degree. rotation of the rotor, since the stator electrode and the rotor electrode are formed by split electrodes respectively. In a usual variable capacitor, on the other hand, the capacitance is increased from the minimum to the maximum upon 180.degree. rotation of a rotor. Therefore, the aforementioned variable capacitor has small resolution in capacitance adjustment, and the capacitance is relatively hard to adjust.
Further, the rotor forming the rotor electrode, which is formed by split electrodes, must be made of an insulating material such as ceramic or resin. In a usual variable capacitor, on the other hand, such a rotor is made of a metal to integrally form a rotor electrode. In the aforementioned variable capacitor, therefore, a working step for obtaining such a rotor is complicated as compared with the usual one.
In addition, the cover for rotatably storing the rotor is provided with no spring for pressing the rotor against the stator. Therefore, dimensional dispersion of the cover, the rotor and the stator appears as dispersion in force for pressing the rotor against the stator, and hence the torque of the rotor and the capacitance may be instabilized.
Accordingly, another object of the present invention is to solve the aforementioned problems in a variable capacitor comprising a stator which is formed by a ceramic dielectric having a stator electrode provided therein.